Key Points

A Doppler assessment is not diagnostic of venous ulceration but may be of
value in defining a safe level of compression bandaging.

Although helpful in defining when compression bandaging is
contraindicated, an ABPI is meaningless when used in isolation.

The majority of patients diagnosed with so-called 'mixed ulcers' in fact
have ulcers of venous aetiology and develop arterial insufficiency over
time.

All patients with an ABPI of less than 0.8 should be referred for
specialist assessment.

In those patients for whom high compression bandaging is contraindicated,
reduced compression may be appropriate in selected cases with further arterial
investigations if the ulcer fails to respond to treatment.

Abstract

An ankle brachial pressure index (ABPI) of 0.8 is seen by some as a
definitive decision-making number and it has almost become the 'Holy Grail' of
leg ulcer assessment. However, its pivotal position is not based on hard
evidence and the time has perhaps come to question our reliance on 0.8 and to
look again at the concept of the mixed ulcer.

What is in a number?

In the case
of 0.8 a lot. An ankle brachial pressure index (ABPI) of 0.8 has become a
pivotal figure in the management of leg ulceration, defining the cut off point
for high compression bandaging and is frequently taken as indicating the
presence of a so-called 'mixed ulcer'. The ABPI is derived from the ratio of
arm systolic pressure, taken as the best non-invasive estimate of central
systolic pressure, and the highest ankle systolic pressure, as measured in each
of the three named vessels at the ankle, for each
limb [1][2]. Details of the method
to be used are given in Box 1.

The use of hand-held
continuous wave Doppler ultrasound equipment to measure systolic pressure and
ABPI calculation is now considered a mandatory part of the assessment of leg
ulcer patients [3][4]. It is a
misconception that an ABPI of > 0.8 is diagnostic of a venous ulcer as at
present there is no diagnostic test for venous ulceration. Rather the diagnosis
is one of exclusion based on the presence of venous disease and the absence of
other aetiological factors. Even in expert hands a proportion of ulcers
labelled as venous will have no detectable venous
disease [5][6]. Although an ABPI of
0.8 may be helpful in defining an arbitrary cut off point for the use of high
compression bandaging, it is however meaningless when used to define an ulcer
category. Early work with Doppler established that a 'normal' ABPI was usually
greater than or equal to 1 and that an ABPI of < 0.92 indicated the presence of arterial
disease [7]. In practice it is rare to find ulceration
caused by arterial disease in a limb with an ABPI of > 0.5, although a low
ABPI may reduce treatment options or delay healing in any leg wound or ulcer
irrespective of its aetiology.

ABPI and 'mixed ulcers'

The importance
of the interaction of venous and arterial disease in the ulcer process has been
recognised for a number of years.
Cornwall [8][9][10],
reporting the Harrow experience, was among the first to suggest the use of
Doppler ABPI measurement in the assessment of patients with leg ulceration.
Both Creutzig et al[11] and
Schultz-Ehrenburg [12] recognised the need for special
guidelines for the management of mixed venous arterial ulcers.
Cornwall et al[13] considered that an
ulcer occurring in a limb with an ABPI of less than 0.9 should be considered
ischaemic and that a pressure index below 0.75 had a significant impact on
clinical management. This paper would appear to be the first reference linking
ABPI to compression therapy. Callam et
al[14][15] reported on
the incidence of skin necrosis and amputation due to compression and recognised
both the concept of 'mixed' ulceration (ulceration in a limb with both venous
and arterial disease) and the need for reducing the compression levels in
patients with an ABPI of 0.7 or less. The authors recognise however that this
was a somewhat empirical approach which needed further study. The study, as far
as the literature shows, has never been conducted. Blair et
al[16] reported a large venous ulcer study
using high compression therapy. In this seminal paper, patients were excluded
from receiving high compression bandages when the ABPI was less than 0.8 as
this group were felt to be at risk of necrosis from high compression bandaging.
No rationale was given as to why 0.8 was used as a cut off point and yet an
ABPI of 0.8 has become the accepted endpoint for high compression therapy, the
trigger for referral for a vascular surgical opinion and the defining upper
marker for an ulcer of mixed aetiology. This reliance on an ABPI of 0.8 was
restated in the nursing literature by Cornwall [17] and
has been stated on many occasions since.

Venous disease is common, and becomes more common with
increasing age. It is therefore not surprising that venous leg
ulceration may at times coexist with arterial
disease. Nelzen et al[18]
in a cross-sectional population study found that the ABPI was 0.9 or
less in 185 (40%) of ulcerated legs. Venous insufficiency was the
dominating causative factor in 250 legs (54%), of which 60% was the
result of deep venous insufficiency. Arterial insufficiency was judged
to be the possible dominating factor in 12% and 6% of limbs clearly
showed ischaemic ulcers. Ghauri et al[19]
found a 17% incidence of co-existing
arterial and venous disease while Liew and
Sinha [20] identified 13% and Scriven et
al[21] 14% of patients with 'mixed'
ulcers. Yet, is it correct to regard these patients as having mixed
ulcers? The term implies that the ulcer has a dual aetiology. The work
of Simon et al[22],
however, would contradict this and suggests that over time a patient
with a venous ulcer may have a slowly reducing ABPI. When reviewing
patients with healed venous ulceration over a 12 month period they
found that in 29% of patients, the ABPI fell over time and that seven
patients (9%) developed arterial insufficiency as defined by an ABPI
of less than 0.8. This drift towards arterial insufficiency over time
is recognised in the recommendations to reassess patients receiving
any form of compression at regular three monthly intervals, or earlier
if symptoms change [3][4]. Fowkes and Callam [23]
in a study comparing leg ulcer patients with age and sex matched
controls concluded that arterial disease was found no more frequently
in venous ulcer patients than in controls, suggesting that arterial
disease is not a risk factor for chronic leg ulceration.

It is likely therefore that the majority of patients diagnosed
as having 'mixed ulcer' in fact have ulcers of venous aetiology, but
that the use of high compression bandaging is contraindicated.
Figure 1
illustrates the therapeutic continuum that should be considered when
treating patients with vascular lower limb ulceration. Over time
patients will progress down the slope as the ABPI falls with
increasing age.

Figure 1 - Relationship between ABPI and
compression

ABPI and
implications for treatment

Clearly it is wrong to regard 0.8 as an
absolute cut off point as it neither defines the transition between venous and
arterial ulceration nor takes into account differences in perfusion pressure
between the three vessels at the ankle - a pressure difference of 15 mmHg or
greater indicates a proximal stenosis or occlusion in the vessel with the lower
pressure [7]. Such a pressure difference will increase the
risk of pressure damage to the related zone of the calf irrespective of the
calculated ABPI for the limb. Recent work by
Carser [24] also casts doubt on the reliance on a single
value as a cut off point for treatment. This study demonstrates how variations
in systolic pressure impact on the calculated ABPI, showing that patients with
a low brachial systolic pressure have a higher mean ABPI and that reference to
accepted criteria for high compression therapy in such a situation may lead to
inappropriate compression and bandage damage.

Reliance on a single ratio also fails to take into consideration other
factors that may be important when defining the level of compression to apply
to any particular limb. These factors include: the limb shape; the presence of
bony prominences; skin condition; the variability within the pressure
measurement between the three ankle pulses; the presence of other diseases such
as diabetes or rheumatoid arthritis; and the patient's tolerance of
compression. In the group for whom high compression is considered inappropriate
the treatment options are:

To correct the underlying arterial disease and then
apply compression [19]

To use an alternative treatment such as
intermittent pneumatic
compression [26][27] or alternative
bandage systems such as short stretch [28].

UK national guidelines suggest that all
patients with an ABPI below 0.8 should receive the benefit of specialist
assessment [3][4]. In our clinic,
which acts as a tertiary referral centre, treatment is a joint decision between
the vascular surgeon and the nurse specialist and is based on assessment and
investigations. Arterial duplex ultrasonography provides a convenient
non-invasive initial assessment method for these
patients [25].
Figure 2
illustrates our management
strategy.

Figure 2 - Management pathway for patients with reduced ABPI

In patients with a reduced ABPI, a history of intolerance of compression
or in whom there is a concern over the immediate introduction of high
compression, such as in a diabetic patient with a marked peripheral neuropathy,
we introduce three-layer compression omitting the third 3a bandage (Elset,
Litepress or K-Lite) of the standard four-layer system. This method is favoured
by Guest et al[25], preferring this
to the 'slack' four-layer system suggested by Ghauri et
al[19], which compromises on the durability of
the bandage system. Short stretch bandages have been advocated in this
situation [28] but our experience suggests that the
majority of these patients are insufficiently mobile to benefit from this form
of compression. If compression is not tolerated, or the ulcer shows little or
no sign of healing within six weeks we would proceed to duplex ultrasonography
and/or arteriography with a view to angioplasty or surgery if
feasible.

In our experience the majority of patients with a
so-called 'mixed ulcer' often present with a previous ulcer history extending
back over several decades. In such patients we would introduce reduced
compression resorting to further arterial investigations only if the ulcer
failed to respond to this treatment, the ABPI continued to fall or is below 0.5
at presentation, or the patient's symptoms, such as claudication or rest pain,
required intervention. Patients presenting with primary lower limb ulceration
and an ABPI of 0.5 or less, even if they have varicose veins or deep venous
insufficiency, should be treated from the onset as having arterial ulcers. In
these patients venous disease, especially if associated with
lipodermatosclerosis or atrophy blanche, should be treated as a secondary event
once the arterial insufficiency is corrected.

There will remain a few cases
which fall outside of these two groups. In these patients we generally use
reduced compression as the primary treatment if the ABPI is above 0.5, but only
after fully evaluating the patient and their limb perfusion. In some cases this
will entail a duplex ultrasound arterial assessment or arteriography. Some
patients do not respond to compression and will be unsuitable for arterial
intervention. In this group we would advocate the use of alternative treatments
such as bed rest or intermittent pneumatic compression with the device set to
the individual's needs and tolerances.

Conclusions

Inappropriate use of high compression bandaging is dangerous and may
place a limb at risk of damage and possibly even amputation. It is therefore
important that these dangers are minimised. Doppler ABPI remains one of the
cornerstones of the assessment process aimed at reducing bandage pressure
damage, but it is only one element in the overall assessment of the patient
and must not be used in isolation.

Box 1: ABPI procedure model
using Doppler method

Explain the procedure and reassure the patient and ensure that he/she is
lying flat and is comfortable, relaxed and rested with no pressure on the
proximal vessels.

Measure the brachial systolic blood pressure:

Place an appropriately sized cuff around the upper arm

Locate the brachial pulse and apply ultrasound contact gel

Angle the Doppler probe at 45 degrees and move the probe to obtain the
best signal

Inflate the cuff until the signal is abolished then deflate the cuff
slowly and record the pressure at which the signal returns being careful not to
move the probe from the line of the artery

Repeat the procedure for the other arm

Use the highest of the two values to calculate the ABPI

Measure the ankle systolic pressure:

Place an appropriately sized cuff around the ankle immediately above the
malleoli having first protected any ulcer that may be present

Figure 3 - Measuring ankle pressure in the dorsalis pedis artery. Note
that the cuff is placed at the ankle. The ulcer is protected by dressings and
cling film

Continue as for the brachial pressure, recording this pressure in the
same way

Repeat this for the posterior tibial
(Figure 4)
and if required the
peroneal arteries

Figure 4 - The posterior tibial artery lies just behind the medial
malleolus. Reflux can frequently be heard in the adjacent veins and this can
help to locate the artery

Use the highest reading obtained to calculate the ABPI for that
leg

Repeat for the other leg

Calculate the ABPI for each leg using the formula below or look up the
ABPI using a reference chart (available as an Excel, Lotus WK3, or CSV file).
This is also presented as an equation -
see Equation 1 below.

Equation 1 -
Calculating ABPI

ABPI normally
> 1.0

ABPI < 0.9 indicates some arterial disease

ABPI > 0.5 and < 0.9 can be associated with claudication and if
symptoms warrant a patient should be referred for further assessment

ABPI < 0.5 indicates severe arterial disease and may be associated
with gangrene, ischaemic ulceration or rest pain and warrants urgent referral
for a vascular opinion

Problems and errors may arise if:

The cuff is repeatedly inflated or inflated for long
periods

This can cause the ankle pressure to fall

The cuff is not placed at the ankle

Ankle systolic pressure is not measured, pressure recorded is usually
higher than ankle pressure

The pulse is irregular or the cuff is deflated too
rapidly

The true systolic pressure may be missed

The vessels are calcified (associated with diabetes), the legs are large,
fatty or oedematous, the cuff size is too small, or the legs are
dependent

Inappropriately high reading will be obtained

Central systolic pressure may influence the 'normal' range for the
ABPI [24]

A defined range for normal and abnormal ABPI has been established and
the deficiencies of the technique noted. These
include:

Reliance on the arm systolic pressure as
the best estimate of central systolic pressure.
Carter [29] and Sumner [7] comment
that arterial disease can exist in the upper limb. Measuring the pressure in
both arms and using the higher of the two pressures increases the non invasive
accuracy of measurement of central systolic pressure but will not eliminate
this potential flaw in the method

Influence of patient positioning on the
results [30]. Lying the patient supine reduces the
hydrostatic pressure inaccuracies. Any deviation would require correction for
the differences

The need for resting and the effect of exercise.
Yao [31] observed that up to 25 minutes rest was the time
needed for severe multilevel arterial disease patients to recover following
exercise

Reliability and ability to reproduce results both over time and between
observers was tested and found to vary by 0.06 which is considered
acceptable [7][30]

Strict requirements for accurate technique including the cuff size,
position and probe
selection [30][32]

Variability of pressure between ankle vessels and its relationship to
proximal occlusive
disease [7][29]

When calculating ABPI using the Doppler method meticulous attention to
detail is necessary to obtain valid measurements [29]; a
lack of awareness of the limitations of the ABPI leads to conflicting results
and misinterpretation of data. When the procedure is followed correctly with
proper consideration of the factors involved (see above), the medical
literature would indicate that this is a safe and reliable method of monitoring
arterial disease. The accuracy along with the limitations have been well
researched and continuous wave Doppler is now accepted as routine practice by
the medical profession.